How to Format numbers with commas in Javascript

For example:

1234 //1,234
1234567890 //1,234,567,890

You can use regular expression

function formatNumber(value) {
    // Add commas to the integer part using a regular expression
    return value.toString().replace(/\B(?=(\d{3})+(?!\d))/g, ",");
}

The regular expression \B(?=(\d{3})+(?!\d)) finds positions in the integer part where commas should be inserted.

This is the best way to help you print an integer with commas as thousands separators.